Optical devices and systems often employ an array of micro-machined mirrors, each mirror being individually movable in response to an electrical signal. In some systems, each of the mirrors can each be cantilevered and moved by an electrostatic force. In one implementation, mirror arrays can be used as optical cross connects in an optical communication system. Generally, each mirror of the cross-connect device may be addressed by a number of electrical leads. In operation, one or more mirrors may receive a beam of light from, for example, an individual optical fiber in a fiber optic bundle. The beams of light reflected from the mirrors may be individually directed to a pre-specified location (e.g., a particular output fiber within an fiber optic bundle array) by individually moving the appropriate mirrors.
To optimize a device's optical transfer ability, it is typically desirable to densely arrange the individual mirrors. However, closely spacing the mirrors is problematic for a variety of reasons. For example, each mirror typically requires some type of supporting structure which may occupy a considerable amount of space. The required electrical interconnections also limit the mirror density. As the number of mirrors in a MEMS array increases, the number of electrical lead lines also increases and must be crowded into already confined spaces. For example, a 256 count mirror device (16.times.16 array) with four electrical leads per mirror would require 1024 separate electrical interconnections.
The number of mirror arrays that may occupy a particular sized chip is therefore subject to limitations based on the physical limits as to how small the leads can be made and how closely they can be spaced apart from each other. Currently, the number of mirrors that may be fabricated on a device is limited because of the above-described physical limitations.
Attempts to increase the number of mirrors on a MEMS device typically result in either an increase in the size of the MEMS device or a decrease in the size of the individual mirrors. However, larger sized MEMS devices and smaller mirrors are often undesirable in many applications.
In view of the foregoing, a present need exists for an optical device that may include a larger array of mirrors, while not sacrificing the necessary mirror spacing or increasing the overall device size.
The problem of designing or assembling the optical controller is much simplified compared to the MEMS device because there is more area in the optical controller to place wires or control circuitry. The optical controller may be built with multi-layer printed circuit boards, for example, so the controller wires may easily be laid on top of each other to cross over to the center of the array. Multiplexing circuitry with digital addressing techniques may be used to reduce the number of required control lines in the optical controller, which is not currently possible with the MEMS electrodes. A third technique would be to use a much larger physical area for the optical controller to accommodate the many control wires, and optically reduce the optical control signals to match the MEMS pattern. This may be done using a single large lens to focus the optical control signals to the MEMS detectors, or use flexible fiber optics to carry the optical control signals from a large, remote location to the MEMS detectors.